cave - add extra output to cave show

Description

Currently cave show -k KEYWORDS shows only 2 versions of package:
installed package and best-version-from-installable

It would be very beneficial for arch teams to be able to see more keywords in more repos.

so having options like:
cave show -k KEYWORDS --best-versions PACKAGENAME
would display keywords line for best version in each repository (not only best-version-in-installable like right now). The only way to achieve it right now is to run cave show -k KEYWORDS package::repo1 && cave show -k KEYWORDS package::repo2 etc

another options would be:
cave show -k KEYWORDS --all-versions PACKAGENAME
would display keywords line for every version in each repository. Output would be very verbose - similar to adjustix -k but for each installable repo. Mixing it with SLOTS
cave show -k KEYWORDS --all-versions PACKAGENAME:2
would reduce output to only matching versions